1. Field of the Invention
The present invention relates to an ISDN communication apparatus which can receive data and signals of a plurality of terminals from an ISDN (Integrated Services Digital Network) line or transmits such data and signals to the ISDN line, and particularly to an ISDN communication apparatus which can transmit a call or receive a call from an originating subscriber even when all B channels are busy.
2. Description of the Prior Art
In the ISDN communication apparatus, setting of communication route for the distant subscriber is executed by a D channel for data communication through line exchange and data transmission has been executed in the transmission rate of 64 kbps using the B channels. When amount of the data is large, data communication has been performed using a plurality of B channels. In a basic ISDN communication, the B channels have B1 and B2 channels.
For example, the Japanese Patent Application Laid-Open No. HEI 6-125343 describes an ISDN communication apparatus having the function to execute communication by multiplexing data with line exchange and to compensate for time difference of data transmission between channels.
The ISDN communication apparatus of the related art is capable of executing only the bilateral communication with a distant communication apparatus using a plurality of B channels such as B1 and B2 channels. Therefore, when the B channels in the communication line, connected to a destination ISDN communication apparatus of a call terminating side, are busy, even if a distant ISDN communication apparatus of a calling side desires to make communication with the destination ISDN communication apparatus, it is impossible to perform the communication. Therefore, if the distant ISDN communication apparatus desires to make an emergency communication, the call from the distant ISDN communication apparatus is not accepted in the destination ISDN communication apparatus until any channel of the B channels becomes idle, and thereby the distant ISDN communication apparatus side cannot transmit important message. Moreover, the call terminating side will lose a very important communication chance.
In addition, when all B channels are busy in the calling side, any call cannot be originated. Accordingly, an operator in the calling side has been requested to be in the waiting condition until at least one channel becomes idle when the operator desires to make emergency data transmission or communication.